1. Field of the Invention
This invention relates to a test device for the detection and measurement of chemical emissions to the atmosphere.
2. Description of Related Art
Industrial components, especially in aging plants, are highly susceptible to gas leaks and the escape of chemical emissions to the atmosphere. As a result, leak detection and measurement is an important safety and cost-saving tool within industrial plants.
A common method that is still employed for detecting leaks is covering a suspect component in soapy water to identify the leak. Alternatively, "sniffer" devices that use a flame ionization detector (FID) or other sensor to detect leaking gas can be used to find and identify the presence of a leak. FIDs are of limited utility for components that are leaking heavily in that if the gas emissions exceed 90,000 ppm the FID "flames out" and must be reset. Neither of the above-described methods is capable of measuring the quantity of the gas emitted but only the concentration of the emitted gas in a plume. Because the concentration of the emitted gas varies significantly with speed and direction of wind, the angle of the probe, the distance of the probe from the leak, the geometry of the leaking component and the flow rate of the sample through the instrument, attempts to correlate the leak rate with the concentration have been unsuccessful. Studies have shown that the scatter in the correlation of leak rate and concentration is 3 to 4 orders of magnitude. Therefore, by using a concentration measurement to determine leak rate, the leak could be calculated at any number between 1 cf per day and 10,000 cf per day.
Early methods for quantification involved bagging a leak and sending the bagged specimen to an off-site lab for testing. This process was time consuming and therefore very expensive. Later, components were bagged and a semi-mobile test device analyzed the sample at the test site.
As taught in Howard, U.S. Pat. No. 5,563,335, a test device was later conceived that drew in an air sample through a sample hose at a high flow rate so as to capture the entire leak and thereupon analyze the concentration of gas emissions within the air sample. By measuring both the concentration in the sample and the concentration in the background air, measurement of the leak rate may be obtained.